PROVIDENCE — How fast is the new 5G data service from Verizon Wireless? It depends.

Are you indoors or outdoors? Are you standing on the north or south sides of the street? And how’s the weather?

You rarely worry about such stuff with a standard 4G smartphone. But last week in Providence, as I tested Verizon’s first 5G system in New England, these questions came up all the time. Expect more of the same when Verizon 5G arrives in Boston later this year.

Verizon let me borrow a $1,300 Samsung Galaxy S10 5G, one of the first phones designed for the company’s new network, and take a stroll through the College Hill area adjoining Brown University,

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Verizon spokesman Andy Choi pointed to an unobtrusive white box atop a lamppost near Thayer Street and Lloyd Avenue. Here, he promised me the full 5G effect. And Verizon came through. The standard Ookla Speedtest app showed a download speed of 1.3 gigabits per second. For a more practical demonstration, I logged onto Netflix, and randomly picked a movie to download — the Margaret Thatcher biopic “The Iron Lady.”

But things got less than optimal once Choi and I started to move. Millimeter wave radios have lousy range, compared to traditional cell networks. Verizon makes up for this by scattering multiple towers throughout the College Hill neighborhood. Sometimes it works, but sometimes it doesn’t. And so the mobile data icon on the phone shifted from 5G to 4G and back again as we strolled. Just a couple hundred feet of distance could make a major difference.

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My favorite moment came at the intersection of Thayer and Meeting streets. On the north side of the street, 5G was in full effect. On the south side, the Samsung phone’s screen announced that it had downshifted to 4G. I crossed the street a couple of times, just to make sure. The shift really was that sudden.

To be sure, the phone’s 4G speed was still mighty fast, up to 117 megabytes. At that rate, my “Iron Lady” download would still have come in at under three minutes, a reasonably snappy performance for such a big file, but far short of my 5G fantasies.

With its limited range, using Verizon 5G is like driving a sports car that does 180 miles per hour, but only on even-numbered streets. Move one block over, and suddenly you’re driving a minivan.

Then there was the visit to the Shake Shack at Thayer and Olive streets. There was a 5G antenna less than 500 feet away. And standing on the corner, Speedtest said that the network was slinging data at something like 1.2 gigabits per second.

But then I stepped inside for a salted caramel milkshake. Even though I could still see the antenna through the restaurant’s expansive windows, my data speed plunged to 4G levels — less than 100 megabits. The 5G signal couldn’t survive contact with a quarter-inch of glass.

Great milkshake, though. And it helped keep me cool. However, the Galaxy 5G phone, now tucked into a shirt pocket, had become almost incandescently hot.

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When you run 5G flat-out, the S10 is transformed from a mere cellphone to a portable furnace. To prevent permanent damage, the S10 drops out of 5G mode into 4G to cool off. (Even the non-5G version of this phone has a reputation for overheating.)

This means 5G performance can vary with the weather. I tried the phone on a fairly hot day, with temperatures in the high 80s, so it got little chance to cool off. Choi told me that the heat might explain the occasional dropoff in download speeds.

This doesn’t appear to be an issue with just Samsung phones. Reportedly, LG phones are also running hot. The issue has been reported on the 5G networks of AT&T and T-Mobile as well.

So 5G phones dislike hot weather, and Verizon’s signal can barely penetrate walls and windows. That’s quite the combination — for people who live outdoors in the dead of winter. But what about the rest of us?

Verizon is deploying a version of 5G that’s right on the edge of current technology, and deploying it fast. It hopes to build an insurmountable lead over rivals AT&T, Sprint, and T-Mobile. And it could work. Sure, service is spotty now. But it’s early days. If Verizon provides respectable coverage in Providence, Chicago, and Boston over the next year or so, it might win the race.

But the limitations of Verizon 5G leave the door wide open to rivals. AT&T is building out a millimeter wave system too. Meanwhile, Sprint is using lower radio frequencies with longer ranges for its 5G buildout. It can’t move data nearly as fast as the Verizon system — around 300 megabits per second in Sprint’s Chicago network, for example. That’s a fraction of Verizon’s top speed, but do you really need anything faster?

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One day you might. We’re promised advanced multiplayer mobile games with three-dimensional graphics and augmented reality visors. Those will need gigabit-level speeds to work, and so when those games arrive, Verizon’s network designers will look like geniuses.

But till then, Sprint’s slower 5G seems a lot more practical. Its lower frequencies will connect over longer distances, and are supposed to keep you connected, even if you turn a corner, cross a street, or enter a building. That’s what we need: a mobile 5G network that keeps delivering the goods, for when, you know, you’re mobile.

Sprint hasn’t announced a 5G network in Boston, but with its nationwide footprint and its coming merger with rival T-Mobile, it’s bound to turn up here. And having tasted Verizon’s lightning-quick but very limited 5G system, I think Boston will welcome the competition.